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MD studies of methanol confined in the metal-organic framework MOF MIL-88B-Cl

2022; Elsevier BV; Volume: 359; Linguagem: Inglês

10.1016/j.molliq.2022.119252

1873-3166

Siwarut Siwaipram, Philippe A. Bopp, Panyapat Ponchai, Jean-Christophe Soetens, Jun‐ya Hasegawa, Rochus Schmid, Sareeya Bureekaew,

Magnetism in coordination complexes

• The shapes of the inner voids of MOF, MIL-88B-Cl, vary widely. • These variations depend on the loading with methanol. • The structure of the included methanol depends on the shape of the voids. • The methanol structure becomes liquid-like only at the highest loadings. • At low loadings, the dynamics of the methanol is very slow. The lattice of the flexible Metal–Organic Framework (MOF) MIL-88B(Fe)-Cl is strongly modified when it is subjected to methanol vapor, increasing its volume by more than 130 %. We use a newly developed interaction model belonging to the extended MOF-FF family to perform classical Molecular Dynamics (MD) simulations of this MOF with varying amounts of methanol guest molecules. This work focuses on the evolving intermolecular structure of the counterions and guest molecules when their number is increased from 1 to 30 per cavity. Two mobile Cl − -counterions are, on the average, present in each lattice cavity to neutralize the framework charges. At low loadings (in the closed (or semi-closed) systems), the methanol molecules aggregate around these ions, which are themselves pegged, at the time scale of the simulation, to the Fe 3 -centers of the MOF. At loadings just below the transition, such methanol aggregates may link two counterions on opposite Fe 3 -centers, thus preventing the MOF from opening unless more methanol is added. In all closed systems, the methanol self-diffusion is almost two orders of magnitude lower than in the bulk liquid. Once the MOF opens, i.e., at loadings higher than about 12 to 13 methanol molecules per cavity, structural features typical of liquid methanol become more and more apparent. However, the evolution is not monotonous, there is a transitional region up to about 22 molecules par cavity. Increasing the loading further, all features more and more resemble the ones of bulk liquid methanol.